This invention relates to a snowmobile and more particularly to an improved drive belt suspension system for a snowmobile.
As is well known, most conventional snowmobiles employ a drive belt that is driven by the engine through a transmission for propelling the snowmobile along the body of terrain over which it is traversing. The drive belt conventionally runs over a guide rail or guide rail assembly that backs up the portion of the drive belt that engages the ground. This guide rail assembly is suspended by some form of suspension system for suspension movement relative to the frame. Conventionally, the guide rail is suspended by front and rear suspension units each of which load a respective cushioning arrangement. In order to maintain a compact assembly, the suspension units and cushioning elements are generally positioned within the confine of the belt.
A conventional type of snowmobile drive belt suspension system is depicted in FIG. 1 and will be described by reference to that figure in order to explain the problems attendant with the prior art type of construction.
As seen in FIG. 1, the snowmobile is comprised of a frame assembly that is shown partially in phantom and is identified generally by the reference numeral 11. This frame assembly journals a driving sprocket 12 which is driven from an engine through a transmission which are of any conventional type and which engine and transmission are not illustrated.
The drive sprocket is engaged with a drive belt 13 which is suspended for suspension movement relative to the frame assembly 11 by a suspension system, indicated generally by the reference numeral 14 and comprised of a front unit 15 and a rear unit 16. These suspension units 15 and 16 support a guide rail assembly 17 which is primarily comprised of a pair of spaced apart guide rails and which engage the backside of the portion of the drive belt 13 that engages the ground over which the snowmobile is traveling.
The guide rail assembly 17 journals a plurality of backup rollers 18 and a larger, idler roller 19. In addition, further rollers 20 and are carried by the frame assembly 11 so as to define the path over which the drive belt 13 travels.
The front suspension unit 15 includes a pair of links 21 that are pivotally connected at one end to the guide rail 17, via brackets 22. The other end of the links 21 are connected to lever arms 23 that are fixed to a tube 24 that is pivotally carried by the frame assembly 11 for pivoting the levers 23 upon suspension travel of the front of the guide rail 17. These levers are connected by a pivot pin 25 to one end of a combined hydraulic shock absorber and coil compression spring assembly 26. The other end of this assembly is connected by a further bracket 27 to the guide rail 17 so as to load the opposite ends of the assembly 26 upon suspension travel of the front portion of the guide rail 17.
The rear suspension unit 16 includes a pair of first links 28 that have pivotal connections 29 at one end to the sides of the guide rail assembly 17. A further pivotal connection 31 connects the opposite end of links 28 with respective second links 32. The other ends of the links 32 are fixed to a frame tube 33 that is journalled on the frame 11. A bracket 34 is coupled to this end of the links 32 and cooperates to load a second suspension unit 35.
The second suspension unit 35, like the suspension unit 26, is comprised of a tubular shock absorber and surrounding coil spring. The bracket 34 has a pivotal connection 36 to one end of the suspension unit 35. A link 37 connects the other end of the suspension unit 35 with the bracket 34 through a pivot pin 38. The link 37 is connected to a lever arm 39 that is pivoted on a further frame tube 41. Hence, the suspension unit 16 loads both ends of the cushioning unit 35 upon suspension travel of the rear of the drive belt.
It should be readily apparent that this prior art type of construction is quite complicated in nature. Also, because of the manner in which the cushioning units 26 and 35 are positioned within the confines of the drive belt 13, the amount of suspension travel is somewhat limited. It is important to be able to obtain relatively large movements of the cushioning units 26 and 35 and of the guide rail 17 and drive belt 13 relative to the frame 11. By having large suspension travel, small bumps can be softly cushioned and yet larger more severe bumps can be cushioned over a larger stroke and with progressively increasing rates as to improve the ride and handling of the vehicle.
It is, therefore, a principal object of this invention to provide an improved drive belt suspension arrangement for a snowmobile.
It is a further object of this invention to provide a simplified compact and yet highly effective suspension system for a snowmobile drive belt.
It is a yet further object of this invention to provide an improved drive belt suspension system for a snowmobile wherein a single cushioning unit can be provided for damping both the front and rear portions of the guide rail and to obtain large suspension travels and yet have a compact assembly.